The present invention relates in general to optical devices such as optical circulators and optical isolators, and more particularly to optical devices that can be configured as an optical circulator having three, four or any number of optical ports, or as an optical isolator having two optical ports.
As generally known, in an optical isolator, a signal in the forward direction is passed from a first optical port to a second optical port. An optical circulator is a non-reciprocal optical device which allows the passage of light from a first optical port to a second one (as in an optical isolator), while a reverse signal into the second port is totally transmitted to a third port and so on for the remaining port(s) for a so-called circulating operation. Any two consecutive ports of an optical circulator are, in effect, an optical isolator since signals travel only one way.
Optical circulator devices play key roles in fiber optical networking systems and devices, for example, in fiberoptic amplifiers, dense wavelength division multiplexing (DWDM) systems and components and optical add-drop module (OADM) components. Several types of optical circulators have been developed. Examples of current optical circulator devices include those disclosed in U.S. Pat. Nos. 5,204,771; 5,471,340; 5,872,878; 6,002,512; 6,064,522 and 6,052,228. However, manufacturing such conventional circulator devices typically requires precise alignment of each optical element, leading to a low yield and high production costs. Furthermore, such conventional circulator devices tend to be bulky and expensive.
It is, therefore, desirable to provide a compact circulator array that is cost-effective and easily manufactured, and which is capable of routing any number of input signals within one integrated circulating module. It is also desirable that an optical circulator module have optimum performance, i.e., very high isolation, very low polarization dependent loss (PDL), very low polarization mode dispersion (PMD), low insertion loss, very low cross-talk, and high power handling capability. An optical circulator should also be designed for mass production with simple assembly processes.
The present invention avoids many of the problems above and substantially achieves an optical circulator or isolator which has a very high performance and which is easily manufactured. The present invention presents optical devices which are useful for long distance and high data rate communication systems.
The present invention provides optical isolator and circulator devices, and methods for making the same, having two optical ports in isolator embodiments and three, four or any number of optical ports in circulator embodiments.
According to embodiments of the present invention, miniature optical devices, including circulator array devices, are fabricated using thin film coating technology. A typical optical device according to the present invention includes two complementary refraction elements arranged opposite each other along a propagation axis and coupled on opposite ends to first and second polarization orientation elements. First and second polarization beam splitter (PBS) elements are coupled to the first and second polarization orientation elements, respectively. The PBS elements are formed using thin film coating techniques and each includes an array of port coupling regions for coupling to an array of input/output fiber port assemblies. The complementary refraction elements include complementary Wollaston Prism elements or complementary Rochon Prism elements, and may be formed using thin film coating techniques or cut from birefringent crystals. Each polarization orientation element includes a Faraday rotator element, and in some embodiments, each also includes a half-wave plate formed using thin film coating techniques. The Faraday rotator elements are periodically poled in some embodiments using selective poling techniques to create oppositely oriented (bi-directional) magnetic domains so that polarization rotations of 45xc2x0 in both clockwise and counter-clockwise directions can be simultaneously achieved on the same magnetic garnet. Periodically etched half-wave plates are used in some embodiments. Depending on the orientation of the refraction elements and the optical axes of the first and second PBS elements, the constituents of each polarization orientation element are designed and oriented so that the circulator device achieves a circulating operation with optical signals at an input port, i, coupled to one PBS element being passed to an output port, i+1, coupled to the other PBS element in a non-reciprocal manner. In some embodiments, a reflective element replaces one of the PBS elements so as to provide a circulator device having a reflective operation, with an optical signal at an input port, i, coupled to the PBS element being passed to the next consecutive port, i+1, coupled to the PBS element.
According to an aspect of the present invention, an optical circulator device for coupling three or more optical fiber ports is provided. The device typically comprises first and second refraction elements each having a refraction axis perpendicular to a propagation axis, wherein each refraction element is arranged so that light traveling in a forward direction parallel to the propagation axis and having a first linear polarization orientation is refracted by a first angle relative to the refraction axis along a refraction plane defined by the propagation and refraction axes, and light traveling in a forward direction parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is refracted by a second angle along the refraction plane opposite the first angle, wherein the first and second refraction elements are arranged opposite each other relative to the propagation axis, with anti-parallel refraction axes and with parallel refraction planes so that light refracted by one refraction element is refracted back parallel to the propagation axis by the other refraction element. The device also typically comprises first and second polarization orientation elements coupled to opposite ends of the first and second refraction elements, respectively, and first and second polarization beam splitting (PBS) films deposited on said first and second polarization orientation elements, respectively, wherein the end face of each of the first and second PBS films opposite the polarization orientation elements defines one or more port coupling regions each for coupling light signals from an optical fiber port, wherein the first and second PBS films are dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light. The first polarization orientation element is typically arranged with respect to the first refraction element and the first PBS film so as to orient the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region on the first PBS film parallel to the first linear polarization orientation so that both beams are refracted by the first angle by the first refraction element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other. The second polarization orientation element is typically arranged with respect to the second refraction element and the second PBS film so as to orient the polarization of both of the parallel light beams of a second optical signal propagating along a forward direction from a second port coupling region on the second PBS film parallel to the second linear polarization orientation so that both beams are refracted by the second angle by the second refraction element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are mutually perpendicular. In operation, therefore, the first optical signal passes from the first port coupling region to the second port coupling region, and the second optical signal passes from the second port coupling region to the third port coupling region.
According to another aspect of the present invention, an optical circulator device for coupling three or more optical fiber ports is provided. The device typically comprises first and second refraction elements each having a refraction axis perpendicular to a propagation axis, wherein each refraction element is arranged so that light traveling in a forward direction parallel to the propagation axis and having a first linear polarization orientation is refracted by a first angle relative to the refraction axis along a refraction plane defined by the propagation and refraction axes, and light traveling in a forward direction parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation is refracted by a second angle along the refraction plane opposite the first angle, wherein the first and second refraction elements are arranged opposite each other relative to the propagation axis, with anti-parallel refraction axes and with parallel refraction planes so that light refracted by one refraction element is refracted back parallel to the propagation axis by the other refraction element. The device also typically includes first and second polarization orientation elements coupled to opposite ends of the first and second refraction elements, respectively, and a polarization beam splitting (PBS) film deposited on said first polarization orientation element, wherein the end face of the PBS film opposite the first polarization orientation element defines three or more port coupling regions for coupling light signals from two or more optical fiber ports, wherein the PBS film is dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light. A reflection element is coupled to the second polarization orientation element opposite the second refraction element, wherein the reflection element is arranged such that the beam components of a light signal propagating in the forward direction are reflected back in the reverse direction. The first polarization orientation element is typically arranged with respect to the first refraction element and the PBS film so as to orient the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region on the PBS film parallel to the first linear polarization orientation so that both beams are refracted by the first angle by the first refraction element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other. The second polarization orientation element rotates the polarization state of each of the parallel light beams of the first optical signal propagating along the forward direction by 45xc2x0 in one direction, and wherein the second polarization orientation element rotates, by 45xc2x0 in the same direction, the polarization state of both of the parallel light beams of the first optical signal propagating along the reverse direction after being reflected by the reflection element such that both beams are parallel to the second linear polarization orientation, and such that both beams are refracted by the second angle by the second refraction element. In operation, therefore, the first optical signal passes from the first port coupling region to the second port coupling region, and the second optical signal passes from the second port coupling region to the third port coupling region.
According to yet another aspect of the present invention, an optical circulator device for coupling three or more optical fiber ports is provided, which typically comprises first and second refraction elements each having a refraction axis perpendicular to a propagation axis, wherein each refraction element is arranged so that light traveling in a forward direction parallel to the propagation axis and having a first linear polarization orientation is refracted by a first angle relative to the refraction axis along a refraction plane defined by the propagation and refraction axes, and light traveling in a forward direction parallel to the propagation axis and having a second linear polarization orientation perpendicular to the first polarization orientation passes through unrefracted, wherein the first and second refraction elements are arranged opposite each other relative to the propagation axis, with anti-parallel refraction axes and with parallel refraction planes so that light refracted by one refraction element is refracted back parallel to the propagation axis by the other refraction element. The device also typically comprises first and second polarization orientation elements coupled to opposite ends of the first and second refraction elements, respectively, and first and second polarization beam splitting (PBS) films deposited on said first and second polarization orientation elements, respectively, wherein the end face of each of the first and second PBS films opposite the polarization orientation elements defines one or more port coupling regions each for coupling light signals from an optical fiber port, wherein the first and second PBS films are dimensioned and arranged so as to split a light signal in a forward direction into two parallel beams of light linearly polarized perpendicular to each other, and to combine parallel beams of light linearly polarized perpendicularly to each other in the reverse direction into a single beam of light. The first polarization orientation element is typically arranged with respect to the first refraction element and the first PBS film so as to orient the polarization of both of the parallel light beams of a first optical signal propagating along a forward direction from a first port coupling region on the first PBS film parallel to the first linear polarization orientation so that both beams are refracted by the first angle by the first refraction element, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are polarized perpendicular to each other. The second polarization orientation element is typically arranged with respect to the second refraction element and the second PBS film so as to orient the polarization of both of the parallel light beams of a second optical signal propagating along a forward direction from a second port coupling region on the second PBS film parallel to the second linear polarization orientation so that both beams pass through the second refraction element unrefracted, and to orient the polarization of two beams linearly polarized parallel to each other propagating in the reverse direction so that they are mutually perpendicular. In operation, therefore, the first optical signal passes from the first port coupling region to the second port coupling region, and the second optical signal passes from the second port coupling region to the third port coupling region.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.